package com.test3;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Util {

	/**
	 * 
	 * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符
	 * 
	 */

	protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e',
			'f' };

	protected static MessageDigest messagedigest = null;

	static {

		try {

			messagedigest = MessageDigest.getInstance("MD5");

		} catch (NoSuchAlgorithmException e) {

			e.printStackTrace();

		}

	}

	public static String getFileMD5String(File file) throws IOException {

		InputStream fis;

		fis = new FileInputStream(file);

		byte[] buffer = new byte[1024];

		int numRead = 0;

		while ((numRead = fis.read(buffer)) > 0) {

			messagedigest.update(buffer, 0, numRead);

		}

		fis.close();

		return bufferToHex(messagedigest.digest());

	}

	public static String getStringMD5(String str) {

		byte[] buffer = str.getBytes();

		messagedigest.update(buffer);

		return bufferToHex(messagedigest.digest());

	}

	public static String bufferToHex(byte bytes[]) {

		return bufferToHex(bytes, 0, bytes.length);

	}

	private static String bufferToHex(byte bytes[], int m, int n) {

		StringBuffer stringbuffer = new StringBuffer(2 * n);

		int k = m + n;

		for (int l = m; l < k; l++) {

			appendHexPair(bytes[l], stringbuffer);

		}

		return stringbuffer.toString();

	}

	private static void appendHexPair(byte bt, StringBuffer stringbuffer) {

		char c0 = hexDigits[(bt & 0xf0) >> 4];// 取字节中高 4 位的数字转换

		// 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同

		char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换

		stringbuffer.append(c0);

		stringbuffer.append(c1);

	}

}
